1. Field of the Invention
The present invention relates to a method of setting up a layer-structured path constructed from multiple layers of paths, and a node apparatus for implementing the same.
2. Description of the Related Art
To transfer packets such as IP (Internet Protocol) packets at high speed, there has been developed a technology known as MPLS (Multiprotocol Label Switching) in which label information is attached to each packet in addition to the header information contained therein and the packet is transferred based on the thus attached label.
A relay apparatus (router) maintains a label table which indicates an outgoing label and an outgoing interface corresponding to the incoming interface and the incoming label. The relay apparatus that receives a packet with a label attached to it converts the incoming label into an outgoing label by using the label table, and outputs the packet on the outgoing interface. This simplifies packet header processing and achieves high-speed packet transfer. The MPLS technology offers the further advantage that, by using a layer-structured label and grouping a plurality of transfer units together, efficient packet routing can be achieved.
A packet transfer procedure using the layer-structured label scheme will be described below. FIG. 1 is a diagram showing how a packet is transferred from relay apparatus 1 to relay apparatus 5. As shown, a path 12 connecting between the relay apparatuses 1 and 3 using L1 labels a and b and a path 14 connecting between the relay apparatuses 3 and 5 using L1 labels a and b are established as lower-layer paths (L1 paths) in MPLS. In addition, an L2 path 16 using L2 labels A and C is established as a higher-layer path (L2 path) passing above the two L1 paths 12 and 13.
The packet transmitting relay apparatus 1 transmits a packet 18 by attaching the label A for the L2 path and the label a for the L1 path to the packet header. The relay apparatus 2 that received the packet 18 through the incoming interface 1 converts the L1 label a attached to the packet 18 into the L1 label b by referring to the label table 20, and transmits the thus labeled packet 22 onto the outgoing interface 2. The relay apparatus 3 that received the packet 22 through the incoming interface 1 converts the L1 label b and L2 label A attached to the packet 22 into the L1 label a and L2 label C by referring to the label table 24, and transmits the thus labeled packet 26 onto the outgoing interface 2. The relay apparatus 4 that received the packet 26 through the incoming interface 1 converts the L1 label a attached to the packet 26 into the L1 label b by referring to the label table 28, and transmits the thus labeled packet 30 onto the outgoing interface 2. The relay apparatus 5 receives the packet 30, with the L1 label a attached to it, through the incoming interface 1.
The label distribution protocol shown in FIG. 2 is used to construct the label tables used for packet forwarding.
In FIG. 2, the source node 1 requesting a path setup transmits a label request message 32, specifying the route (relay nodes) to the path terminating node 4, hop by hop, to the path terminating node. Then, the terminating node 4 returns a label mapping message 34 for label mapping, to the source node 1. Using this label mapping message, the label mapped according to the label request is notified to each subsequent node.
This label distribution protocol has the function of only distributing a single-layer label. To construct an L2 path, therefore, the procedure requires that L1 paths necessary for the construction of the L2 path be established in advance by using the label distribution protocol. Then, using the label distribution protocol again, the L2 path is constructed above the thus established L1 paths.
In an optical network constructed using OXCs (Optical Cross Connects) and WDM (Wavelength Division Multiplexing), one optical wavelength is treated as one label, and optical wavelength paths are established by using a protocol created by extending the above-described label distribution protocol. Then, using the label distribution protocol again, an MPLS path is established above the thus established optical wavelength paths.
To construct a new MPLS path above the optical wavelength paths, the optical wavelength paths necessary for the construction of the new MPLS path are established in advance by using the label distribution protocol, as in the case of the L2 path described above. Then, the MPLS path is established above the thus established optical wavelength paths by using the label distribution protocol.
As described above, an L2 path is usually established above already established L1 paths. As a result, when establishing an L2 path along a route over a portion of which L1 paths are not established, L1 paths are established first by using the label distribution protocol, and then the L2 path is established by using the label distribution protocol once again.
Therefore, when establishing an L2 path along a route over a portion of which L1 paths are not established, the label distribution protocol has to be used twice, leading to the problem that it takes time to establish the L2 path because many control messages flow through the network and because the protocol has to be activated in sequence.
In an optical network also, when constructing an MPLS path above optical wavelength paths, a similar problem occurs if there is a portion over which optical wavelength paths are not established.